Method of electrolytically precipitating metals and compounds from solutions



UNITED STATES PATENroFFIc GEORGE D. VAN ARSDALE AND CHARLES G. MAIER, OF NEW YORK, N. Y.

EETHOD OF ELEGTROLYTTGALIY PRECIPITATING METALS AN D COMPOUNDS FROE' SOLUTIONS.

1,371,826. No Drawing.

To all whom it may concern:

Be it known that we, Gnonon D. VAN ARSDALE and CHARLES G. MAmR, citizens of the United States, and residents of New York city, in the county of New York and State of New York, have invented certain new and useful Improvements in Methods of Electrolytically Precipitating Metals and Compounds from Solutlons, of which the following is a specification.

This mvention is an improvement in methods of electrolytically precipitating metals and compounds from solutions.

It'is applicable to those processes inwhich an insoluble anode is used and in which the metal to be recovered is deposited at the cathode, also to processes in which a compound of a metal is separated at the anode and hydrogen evolved at the cathode, and 1s finally of very considerable advantage utilized in cases where two ores of certain kinds are to be treated together.

In the first two cases the use of depolarizing agents is known, but in most cases such depolarization results in the accumulation in solution of the products of depolarization with detriment to further electrolytic eiiiciency. The improvement which we have made, and which may be a plied m a variety of ways, is the use of. epolarizers, the products of whose depolarizing act on are insoluble and therefore do not accumulate in solution, and which also may be recovered by reason of this fact and re-used cyclically in subsequent operations. We have also found several cases in which two products, which are to be recovered, may be so recoveredby electrolysis at the same time in the same cell, one at the anode and one at the cathode, and in which operation they act mutually as depolarizing agents, giving a reduction in voltage and consequent economy in power.

Several special cases in which this invention may be applied are described, but others will be mentioned only, and others again will occur to those skilled in the art, all of which employ this discovery.

In the electrolytic precipitation of copper from solution using insoluble anodes, as a part of a leachingprocess for separating copper from ore, it has been found desirable to use depolarizing agents, both for the pur- 'pose of reducing the' voltage otherwise Specification of Letters Patent.

Patented Mar. 15, 1921.

Application filed May 18, 1913. Serial No. 234,241.

ing anode disintegration which otherwise occurs to a prohibitive degree in the electrolysis of sulfate solutions. Iron salts and sulfur dioxid have been proposed and used separately or in combination for such purposes. Iron, however, is open to some objection since although ferrous sulfate is an efficient anodic depolarizer, the product of its depolarizing action, ferric sulfate, accumulates in the solution during the electrolysis, and rapidly reduces the cathodic eificiency, the practical result being that needed, and also for the purpose of preventv only a small portion of the copper present can be efficiently precipitated at each cycle.

The solution must then be withdrawn from the electrolysis and the ferric iron reduced, or reduction of the ferric iron must be done during the electrolysis both of which are more or less'inconvenient. The present invention provides a means for accompli'shing both of the above purposes in the electrolysis of solutions of copper, namely depolarizing and reduction of voltage, and prevention of disintegration of anodes, and the result of this depolarizing action is a solid product precipitated at the anode. As a consequence of this fact there is no accumulation of the depolarizing product in the solutions, as when iron is used which is evidently of great practical importance. Also the same depolarizer may a used cyclically as described later.

- Our present invention, however, is not only of advantagein this respect as indicated above, and as will be described later, but is also of advantage in the electrolysis of solutions of manganese to produce mansentially in the leaching of manganese ores by suitable reagents to produce manganese sulfate solutions, and the subsequent electrolysis of such solutions, making manganese dioxid at the anode and free sulfuric acidin the electrolyte. Such a process is satisfactory, but is open to the objection that the voltage is high, difiering from the high Volta e in copper electrolysis above mentioned, in that in this case we are concerned with the reactions at the cathode instead of at the anode. In other words what is needed for a more economical electrolytic production of manganese dioxid is a cathodic deled polarizing agent, and We have discovered that copper in solutions of manganese will act very efiiciently as such a cathodic deresult of depolarization at either electrode as in other methods of polarizin agents.

It is evldent that this invention is of value as a part of processes for extracting either manganese or copper or both from their ores either together or separately.

It can be seen that our invention can be utilized in a number of ways, several of which are mentioned and described below. For example, in the recovery of manganese and copper from ores there are three cases- (1st) in which it is desired to treat a manganese ore alone for the recovery of manganese (2nd) in which it is desired to treat a copper ore alone for the recovery of copper; and (3rd) in which it is desired to treat both manganese and copper ores together for the recovery of both manganese and copper.

electrolyzing with de- In all three cases the invention used is the same but the manner of use difl'ers as follows. In the first case above, the copper as sulfate is used cyclically in the recovery of manganese which is removed and marketed; in the second the man anese is used cyclically inthe recovery 0 copper which is removed and .sold; and in the third both I manganese and copper act mutually as dei is a supply of of manganous sulfate,

pollgrlzing agents and are both removed and In all three cases the products of depolarization are insoluble, solid products, produced at the electrodes and not, as in other electrolytic processes, in which depolarization is used, soluble products which accumulate in the electrolyte and by their presence proportionally reduce deposition efliciencies.

One way in which each of the above three possibilities may be carried out for recovering copper and manganese, will now be described.

For the first leaching and electrolytic recovery of manganese, but no available supply cfsu-itable copper ore. The manganese ore is treated so as to obtain a substantially pure solution which may be done as follows: The ore is crushed and suspended in water, to which, if necessary some acid ferric condition case it is assumed that there a manganese ore sultable for .thionates or other compounds objectionable in electrolysis.

This may be done 1n several amount of thionates produced in leaching manganese from its ores by sulfur dioxid will be greatest in cold, neutral solutions, and least in hot, acid solutions. With a solution between 60 and 100 C. and containing from 5% to 10% free sulfuric acid, the amount of thionates will not be enough to interfere with subse uent operations. The solution is then placed in contact with a fresh amount of dioxid manganese ore, without adding'SO,,. v This is for the purpose of oxidizing any iron present to the ferric condition, and also for oxidizing any remaining thionates. The

ways. The

object of changing the iron to the ferric condition is because iron in the ferrous greatly reduces the current efliciency of anode deposition of Mn(),. The ferric iron produced may be enough to interfere with the deposition of copper at the cathode, but this is not important for this of the process, since being entirely in the it may be precipitated and removed. a i

A-solution of copper sulfate is then'added to the solution. of manganous sulfate, the.

copper sulfate being obtained as described later. The solution should contain an amount of copper chemically equivalent to the amount of manganese subsequently separated by the electrolysis, at the anode The solution containing copperand manganese is then referably heated to between 60 and 70 6: and subjected to electrolysis while hot. The usual electrodes and apparatus employed for this purpose may be used.

e refer to use carbon, graphite or coke as ano e material, and as cathodes either copper or iron sheets. The current density may be at any commercially economical point, say 'six amperes persquare foot or more. If the current density is high enough, for example about twenty amperes per square foot, a part or'all of the deposited copper will be in a spongy particular application trolysis of manganese sulfate solution alone dioxid at the would produce manganese 111 the electroanode and free sulfuric acid lyte, but the voltage would be high, and

hydrogen would be evolved at the cathode.

When copper is present under exactly the same conditions no hydrogen is evolved at the cathode, copper being deposited instead, and the result is a considerable decrease in the voltage. After electrolysis has proceeded for a sufiicient lenth of time, depending on the anode and cathode efficiency obtained and the use to which the manganese dioxid and acid produced are to be put, the electrolyzed solution is separated from the dioxid and the latter separated from the anode or otherwise treated and prepared for use as described elsewhere, and fresh portions of original electrolyte are again prepared and subjected to electrolysis, the process being thus made continuous. A por-- tion of the acid produced may be used for treating the ore in case all of the manganese is not soluble, by means of S0,, or acid from an outside source may be added.

During the electrolysis of the solution, as stated above, copper is precipitated at the cathode. If this is precipitated in a spongy form it may be readily detached from the cathode, and is then easily oxidized by heating or otherwise, andafter oxidation is then dissolved in a portion or all of the acid resulting from the electrolysis. The solution thus made may then be used for suspending the crushed manganese ore for the first stage of the process as described above. Variations in the above procedure may of course be made if desired, using the same principles.

For the second case it is assumed that there is a supply of copper ore suitable for leaching, but no available supply of manganese ore in large amounts. In this case the manganese dioxid produced is used cyclically as the depolarizing agent, and the copper becomes the main product to be disposed of,

differing from the first case in which the copper is used cyclically.

Operation may be as follows: The copper ore, in which the copper may be either in the oxidized or sulfid state, is leached by a solution in which the active leaching agents are sulfuric acid and ferric sulfate, and which also contains manganese sulfate. ThlS may be done in any suitable apparatus, preferably some form of counter-current leaching device. The sulfids present will reduce a part or all of the ferric iron to the ferrous condition. This ferrous iron is objectionable in the subsequent electrolysis and is therefore oxidized to the ferric state,

which is accomplished by the MnO produced subsequently. If the ferric iron is present in too large an amount a portion of it may be removed byprecipitation at this point. objectionable for electrolysis and production of copper as in the usual methods, since The ferric iron produced is not so under the conditions of our work a high cur- The solution is now subjected to electrolysis in apparatus arranged for continuous operation. The copper deposited at thecathode is withdrawn from time to time and treated in the same way as electrolytic copper from other electrolytic processes.

The manganese dioxid precipitated at the anode from the manganese sulfate present in the solutions, is also removed from time to time. It is unnecessary-to detach this from the anodes, since it is used to oxidize Fe" to Fe and since MnO is very readily soluble in very weak, acid solutions of ferrous iron, being thereby dissolved and returned to the cycle as described above,

The solution resulting a from the electrolysis will contain ferrous and ferric iron, free acid and any residual copper and manganese.

The current density at the cathode during electrolysis having been maintained sufficiently high to overcome the dissolving action of ferric iron on the copper deposited, and a good efliciency having thus been obtained, the resulting solution will have most of its iron in the ferric condition.

It is desirable for the subsequent leaching which is done with this solution, to have all of'the iron in the ferric state, and this may be done by using a part of the deposited MnO for this purpose, the result being an acid solution with all iron as ferric iron, which is now applied to a fresh portion of ore and the process thus repeated.

For the third case it is assumed that we have available supplies of both copper and manganese ores, suitable for leaching. In the copper ores it is immaterial whether the copper is present as oxid or sulfid. It is important that at least a large amount of the manganese be in the form of dioxid in its ore. Whether acid in addition to that provided by the cycle of operations will be needed or not, depends on the acid consuming character of the ores being treated. If extra acid is needed it may be produced by an additional step of the process to be described later, and as much as required may be made in this way.

The manganese and copper ores to be equivalent to the amount of copper and manganese electrolytically deposited, and any copper and manganese remaining after electrolysis.

The copper and manganese ores being enough free acid for the subsequent treat- Generally speaking for the recovery methods.

treated are brought into contact with thissolution whereby their copper and manganese values are brought into solution, and the resulting solution'is then separated from the tailings, which are preferably washed before being discarded.

If the amount of iron in the solution thus obtained is too reat for proper electrolysis, it may be readi y removed by precipitation or otherwise and the accumulation of impurities may also be provided for at this point by the removal altogether of a part of the solution and the treatment of this of its values by other The solution is now subjected to electrolysis, which is done in the usual form of apparatus, arranged for continuous operation, at current density equivalent to SIX amperes per square foot or more. There will be produced copper at the cathode, and manganese dioxid at the anode, both of which are removed from the tanks from time to time. The copperis deposited on starting sheets made in the usual way, and the cathodes produced are treated the same as cathodes from other electrolytic methods. The manganese may be deposited on graphite or carbon anodes, and subsequently removed from them as described elsewhere, or crushed coke or carbon may be employed as anode material. The electrolysis 1s continued as long as reasonble cathode and anode efliciencies are obtained.

The resulting solution may. not contain ment of freshamounts of ore, and if so a part or all of the ferric ironpresent may be reduced by sulfur dioxid, making equivalent amounts of free acid and ferrous iron,

thelatter being again oxidized to ferric iron by adding ore containing manganese dioxid at this separated from the residue of the manganese ore and will then have all of its iron in the ferric state and be thus available for repeating the procession fresh ores.

It is evident that by the repetition of this last step as much free acid as required may be made at the expense of anaccumulation of manganese.

The above special applications of the process have been fully described. There are in addition a'number of other ways in which the same principles may be utilized. the'soluble salt of any metal capable of forming a metallic compound at the anode, the metal in which is in a higher state of oxidation than it was preration of viously when in solution, may be used as an anodlc depolarizing agent with the described advantages in the electrolytic sepaa metal from solution. Other examples of such metals capable of thus acting under proper conditions are lead, vanadium,

' Lenses point. The solution thus treated isetc. Generally speakingalso in the 1recovery of such metals as last mentioned, by separation at the anode the soluble salt of the'same or another metal capable of giving a metallic deposit at-the cathode instead of the hydrogen which would otherwise be evolved, may

finally, combinations of the depolarizing action at both electrodes as described in the above special case may be used.

Having thus described the invention, what is claimed as new is 1. An improved method of depolarization m use as a epolarizing agent of a metal, a soluble salt of-which is capable as a result of electrolysis, of yielding a metal or metallic compound at an electrode, and removor metallic compound and ing said metal treating'the same to regenerate the salt of the metal originally used as a depolarizing agent in subsequent electrolysis.

2. An improved method of electrolysis which comprises in electrolyzing a solution containing a copper salt capable of producing an insoluble deposit at one electrode,

copper or copper compound being removed and treating the same to regenerate the copper salt originally used as a. depolarizing agent in subsequent electrolysis. v

4. The process of producing copper from its ores which comprises leaching an ore of the metal with a solution containing sulric acid, ferric .sulfate, and a salt of an electro-positive metal, and electrolyzing the.

solution wherebyito obtain a deposit of copper in the metallic state at the cathode, and a deposit of the electro positive metal or an insoluble compound thereof at the anode.

5. The process of producing copper from its ores the metal with a solution containing sul furic acid, ferric sulfate, and a salt of an electro-positive metal, electrolyzing the solution whereby to obtain a deposit of copper in the metallic state at the cathode, and a deposit of the electro-positive metal of an insoluble compound thereof at the anode, removing the anode deposit, and treating the same with /the' solution which results from the step of electrolysis whereby to re generate the salt of the electro-positive metal originally employed, whereby the which comprises leaching anore of.

be used as a depolarizer. And

electrol sis which comprises the cyclical same may be used cyclically as a depolarizing a ent.

6. he process of separating metal values from a composite solution containing an electro-negative metal and an 'electro-positive metal, by a process of electrolysis which comprises leaching ores of the two metals with a solution of sulfuric acid, and, if required, ferric iron, and electrolyzing the solution whereby to obtain a cathodic deposit of the electro-negative metal and an anodic deposit of the electro-positive metal, and in which step of electrolysis the metals mutually act as depolarizing agents.

7. The process of producing copper in the metallic state and manganese dioxid from a composite solution of sulfates of these metals which comprises subjecting such composite solution to electrolysis and thereby efi'ecting an anodic deposition of manganese dioxid and a cathodic deposition of copper in the metallic state.

Signed at New York in the county of New York and State of New York this 17th day of April, A. D. 1918.

GEORGE D. VAN ARSDALE. CHARLES Gr. MAIER. 

